Surge suppressor employing capacitor charging means



Nov. 16, 1965 w. H. NOBIS 3,218,543

SURGE SUPPRESSOR EMPLOYING CAPACITOR CHARGING MEANS Filed Oct. 13. 1961AT 1A 20 g 30 :E .1 56

i 556* 16 i; ji E: 35 zg/Hilyi 60 T E 50 54 E 46 w 5 k L I a :2 1 T 1:4:I 4 4E I United States Patent 3,218,543 SURGE SUPPRESSOR EMPLOYINGCAPACITOR CHARGING MEANS Wilhelm Heinrich Nobis, Merzhausen, nearFreiburg im Breisgau, Germany, assignor to Fritz Hellige & C0.,

G.m.b.H., Freiburg, Germany Filed Oct. 13, 1961, Ser. No. 145,032 Claimspriority, application Germany, Oct. 13, 1960,

40,666 14 Claims. (Cl. 32341) The present invention relates to surgesuppressing circuits, and more particularly to a surge suppressingcircuit for inhibiting the response of an electronic circuit to powersupply interruptions.

In circuits such as oscillators and amplifiers employing either vacuumtubes or transistors, current-responsive resistors (hereinafter referredto as thermistors) are frequently included to stabilize or controloperation of the circuit.

Advantage is taken, in such applications, of the fact that theresistance of a thermistor is determined by the power dissipated in, orthe current through the thermistor. By selecting a thermistor having anappropriate temperature coefiicient of resistance, it is possible tocompensate for variations in the remaining elements of the circuit inoperation.

However, such circuits as developed in the past have frequently sufferedfrom the serious shortcoming that very short power supply interruptionsmay produce output current surges which are detrimental, either tocomponents in the circuits themselves or to apparatus such as a meter orrecorder to which the circuits supply signals. These voltage surgesfrequently reach values which are significantly above those appearingunder normal operating conditions.

If, for example, in a normally operating oscillator, alternating currentgenerator or amplifier, the power supply is interrupted for a shorttime, such as 15-25 seconds, a thermistor forming part of any of thestages of the circuit will have cooled off during this period of timeand returned to its quiescent value of resistance. However, the cathodesof vacuum tubes will ordinarily still be at a temperature sufficientlyhigh to permit electron emission. Under such circumstances restorationof the power supply will produce an output current surge because thevacuum tubes are conductive while the thermistor presents a resistanceother than its normal operating value.

A number of circuits employing thermal or time delay relays haveheretofore been proposed to eliminate current surges of the typedescribed. However, such circuits suffer from the serious disadvantagethat the minimum period of inhibition possible is generally from thirtyto sixty seconds, which may be in excess of that actually required. Atthe same time, such circuits frequently fail to protect against voltagesurges caused by very brief interruptions. Such circuits also frequentlyinvolve switching, which may itself produce transients or surges.Accordingly, there is a definite need for automatically responsive surgeor transient suppressors which operate to inhibit a circuit for a shortperiod no longer than necessary for the circuit elements to return totheir normal thermal conditions.

It is, therefore, an object of the present invention to provide acircuit automatically responsive to power supply interruption tosuppress output current surges or transients which would ordinarilyoccur upon restoration of the power supply within a short period.

A further object of the present invention is to provide a surgesuppressor circuit for inhibiting the response of an electronic circuitfollowing a brief interruption in 3,218,543 Patented Nov. 16, 1965 powersupply to the circuit which operates automatically upon restoration ofpower to the circuit, yet requires no moving parts or switches.

A further object of the present invention is to provide a surgesuppressing circuit which is automatically operative to protect a numberof stages of a multistage circuit from current surges or transients dueto power supply interruption.

A further object of the present invention is to provide a circuit foruse with a vacuum tube or transistor stage to inhibit the response ofthe stage for a period of time following power supply interruption andrestoration not in excess of that necessary to ensure normal operationof the circuit, regardless of how brief the interruption.

In accordance with the invention, a circuit using electron dischargedevices includes circuit elements energized by the voltage supply whenit is restored subsequent to interruption which operate to apply anegative cutoff biasing potential to one of the eletcrodes of one of theelectron discharge devices, the cutoff biasing potential thereaftergradually decreasing over a time sufficiently long to permit the circuitcomponents to return to their normal operating conditions. It will beunderstood that the circuit components permitted to return to theirnormal operating conditions are mainly the cathodes, in the case ofvacuum tube circuits, and, furthermore, thermistors which start heatingup again upon restoration of power supply until their resistance valuereaches that of continued normal operation. It will be clear from theforegoing that an important feature of the present invention, residingin the application of a cutoff bias to an electrode which occurssubstantially instantaneously, inhibits current surges in the outputcircuit of the entire system since the stage of the circuit of which thebiased electrode forms a part is inhibited automatically and graduallyreturns to its normal state of operation.

In accordance with another important feature of this invention, theinhibited stage may be distinct from that which includes the thermistor.In other words, the thermistor may form part of the cathode branch ofthe plate circuit in one stage of a multistage oscillator, alternatingcurrent generator or amplifier, while the stage including the circuit ofthe present invention may be another stage of the same circuit system.Alternatively, the thermistor may form part of a coupling networkbetween stages preceding the stage including the circuit of the presentinvention.

Further features of the present invention include a capacitor which ismaintained under charge when normal circumstances prevail, and means fordischarging the capacitor upon interruption in power supply, so that thecapacitor constitutes a shunt for connecting a negative potential to anelectrode which may be the suppressor grid or the control grid of avacuum tube. It will be apparent that, upon restoration of the powersupply, a strong negative potential appears at the electrode to inhibitthe response of the circuit.

Further features of the present invention include a voltage dividerconnected between the power supply terminals, a capacitor connectedacross one resistor of the voltage divider and arranged to dischargetherethrough upon interruption of power supply, and a diode forming anadditional discharge path for the capacitor. It will readily beunderstood that optimum results are achieved if the capacitor ispermitted to discharge in a very short time. Thus, in accordance with animportant feature of the invention, the time constant of the dischargepath is relatively short. When the power supply is restored, thecapacitor is recharged through the voltage divider, the rechargingcircuit including a relatively high resistance, so that the rechargingcircuit possesses a time constant which is greater by several orders ofmagnitude than the dis charge time constant. Accordingly, as thecapacitor charges at a comparatively low rate, the cutoff biasingpotential applied to the electrode decreases at the same rate, so that athermistor forming part either of the same stage or of another stage, asstated above, returns to its high value resistance before the fulloutput current level is reached and no surges may occur.

It will be clear from the foregoing general description that the surgesuppressor of the present invention operates automatically since it isenergized by the power supply of the system. More specifically, a chargeis maintained on the capacitor under normal operating circumstances, andupon power supply interruption the capacitor discharges automaticallyand substantially instantaneously. In the discharged state, thecapacitor presents a short circuit between the negative power supplyterminal and the grid of the stage to be inhibited, ready to act in theevent power supply reappears regardless of the duration of theinterruption. When power is restored, the capacitor immediately startsrecharging and the cutoff biasing potential also immediately starts todecrease toward its normal value. It is to be noted that the entireoperation is, therefore, controlled by the power supply interruption andnot by the characteristic of a component outside and distinct from thecircuit, as is the case with prior art surge suppressors using, forexample, bimetal strips.

Further features, objects and advantages of the present invention willbe more clearly understood by a consideration of the following detaileddescription and the accompanying drawings in which FIG. 1 is a circuitdiagram of a typical prior art circuit utilized in describing thepurposes of the present invention;

FIG. 2 is a circuit diagram illustrating one embodiment of the presentinvention; and

FIG. 3 and FIG. 4 are circuit diagrams illustrating other embodiments ofthe present invention.

The same or similar elements are designated by the same referencenumerals throughout the several figures of the drawing.

Referring now to FIG. 1, one stage of a prior art circuit forming part,for example, of an oscillator or an amplifier, includes a pentodeelectron discharge device it) having an indirectly heated cathode 12, aplate 14, a control electrode or suppressor grid 16 and a control grid18. Plate 14 is connected to a voltage source 24 through a load resistor28, while cathode 12 is connected to the remaining terminal of voltagesource 24 through a resistor 32. While voltage source 24 is depicted inFIG. 1 and the remaining figures as a battery, it will be understoodthat, in practice, a conventional power supply of relatively lowinternal impedance energized from a commercial source may be employed. Agrid leak resistor 26 is connected between control grid 18 and thenegative terminal of voltage source 24 which may be grounded. Inputsignals to the stage may be applied across a pair of input terminals 20,connected between control grid 18 and ground, while output signals maybe taken from a pair of output terminals 22 connected across load 28 andvoltage source 24.

Feedback energy taken from another stage (not shown) may be applied tothe stage at terminal 30 connected to cathode 12, if the circuit of FIG.1 forms one stage of a more complex circuit.

Considering now the operation of the circuit thus described, resistor 32inserted in the cathode lead of the plate circuit will be assumed to bea thermistor. Upon interruption in plate current supply, thermistor 32will cool off within a very short time period, and if power is suppliedagain after a period of time which is so short that cathode 12 is stillhot, a voltage surge will appear across load resistor 28 and outputterminals 22. This surge may exceed by far that applied to the loadresistor under normal operating conditions when thermistor 32 hasreached its usual operating temperature level. It is well known thatsuch voltage surges cannot occur if the device is started after a longerperiod of non-operation, since the cathode 12 is cold and unable to emitelectrons. The phenomenon described above is well known in the art andhas led to the designs mentioned in the foregoing general description ofsurge suppressors using, for example, bimetal strip-relay combinations.

Referring now to FIG. 2, there is shown a circuit diagram of oneembodiment of a surge suppressor according to the present invention. Asshown in the figure, the circuit comprises input terminals 20, outputterminals 22, grid leak resistor 26, load resistor 28, and feedbackinput terminal 30 and electron discharge device 10 corresponding tothose in FIG. 1. Resistor 34 in the cathode branch of the plate circuitmay be a thermistor having a characteristically low thermal inertiawhich causes the voltage output surges which must be suppressed.However, it is to be understood that resistor 34 need not necessarily bethe current or temperature dependent element of the complete system.Rather, resistor 34 may be a substantially temperature constant circuitelement and any other stage of the complete system may include thethermistor. In other words, the stage shown in FIG. 2 may be combinedwith other stages, such as that of FIG. 1 in which resistor 32 istemperature dependent.

In accordance with the invention, the circuit of FIG. 2 includes anarrangement for applying a suppressing biasing potential to a controlelectrode such as a suppressor gird 16 to suppress voltage surges uponpower supply interruption and restoration. A voltage divider 36connected across power input leads 38 and 40 comprises a comparativelyhigh resistance resistor 42 and a relatively low value resistanceresistor 44, serially connnected to each other at junction 46. Junction46 is connected to suppressor grid 16 and resistors 42 and 44 areselected to provide a normal operating or a slightly negative bias ongrid 16 with respect to cathode 12. A capacitor 48 is connected acrossresistor 44, and the junction 50 of resistor 42, resistor 44 andcapacitor 48 is connected by a diode 52 to a grounded busline 54. Powerfor the plate circuit, as well as the voltage drop across the voltagedivider 36, is supplied from a potential source 56, having a tap 58connected to busline 54. It will be clear that the upper portion 60 ofvoltage supply 56 provides the plate potential for pentode 10 while theentire source 56 energizes the voltage divider 36, so that, under normaloperating conditions, capacitor 48 will be charged to a potentialcorresponding to the voltage drop appearing across resistor 44. Thepotential applied between busline 54 and lead 40 by source 56 should besufiicient to bias tube 10 to cut-ofi when applied between controlelectrode 16 and busline 54 when the circuit operates in its suppressionmode, as will be described hereinafter.

Considering now the operation of the circuit thus described, when powersupply source 56 is interrupted, all of the potential differences in thecircuit will disappear substantially instantaneously. Consequently,capacitor 43 will discharge through resistor 44 and, since the circuitelements involved exhibit a short time constant, discharge occurssubstantially instantaneously. This eliect is enhanced by the presenceof diode 52, since an additional discharge path for capacitor 48 isformed through diode 52, lead 54, the lower portion of power supply 56and lead 40. At this point it should be noted that the circuit would beoperative without employing the diode 52. However, it will readily beunderstood that a short time constant for the discharge of capacitor 44is important inasmuch as the surge suppressor is ready to act when thecapacitor is discharged but not before. With the diode and theadditional discharge path formed by it, the charge on capacitor 48disappears substantially instantaneously, so that, in practice, outputsurges caused even by extremely short supply interruptions areelTectively eliminated.

When the power supply is restored, capacitor 48, now discharged,effectively short circuits resistor 44 of voltage divider 36 so that thevoltage supplied by the lower portion of source 56 is effectivelyapplied directly between suppressor grid 16 and cathode 12. Thepotential applied as discussed constitutes a cutoff biasing potentialwhich inhibits the conduction of pentode 10, so that, at the beginningof this period, practically no plate current may flow and output currentsurges are effectively eliminated.

Once the power supply is restored, the voltage drop reappearing onvoltage divider 36 operates to recharge capacitor 48 through high valueresistor 42. Considering the comparatively long time constant of therecharging circuit, it will be understood that recharging occurs at acomparatively slow rate. At the same time, the potential at junction 46becomes gradually more positive so that the biasing potential applied togrid 16 decreases. As a result, plate current is gradually restored atthe same rate until full plate current and output from the entire systemare reached. It will be clear from the foregoing discussion that duringthis gradual change of conditions in the circuit, the thermistor whichmay be resistor 34 in FIG. 2 or which may be any other resistor in theoutput circuit associated with another stage of the same circuit, willheat up until normal operating conditions prevail.

FIG. 3 illustrates another embodiment of the invention which differsfrom that of FIG. 2 in that the stage comprises a triode electrondischarge device 64 and, in the absence of a suppressor grid, thesuppression of response contemplated according to the present inventionis based on the utilization of control grid 62 as the control electrode.The circuit operates essentially in the same manner as that of FIG. 2,and identical components are designated by the same reference numerals.However, the junction 46 between resistors 42 and 44 of voltage divider36 is connected to control grid 62 through grid leak resistor 26. Itwill be seen that charging the capacitor 48 during normal operation ofthe circuit occurs in a manner identical to that of the circuit of FIG.2. Similarly, both discharge paths for the capacitor 48 are the same inFIGS. 2 and 3 and include, on one hand, the resistor 44 and, on theother hand, diode 52, and the lower portion of tapped voltage source 56.In this embodiment, as well, the additional discharge path through diode52 may be omitted, although the circuit preferably includes the diode,in order to prevent output current surges in the event of very shortpower supply interruptions.

The bias applied to the tube to inhibit its response should, of course,be that appropriate to the use of grid 62 as the control electrode forthe circuit.

FIG. 4 illustrates another embodiment of the invention wherein theautomatic control for eliminating voltage surges is arranged to remove aconductive bias from the tube when the power supply is interrupted. Asshown in the figure, the circuit comprises a separate voltage source 66for the voltage divider 36, which includes a high value resistor 68 anda low value resistor 70. Plate current is supplied from voltage source72, the latter being entirely separate from the voltage divider. Undernormal operating conditions, junction 74 is maintained at a potentialwhich is slightly negative with respect to cathode 76, so that nocurrent flows through diode 52, which should also be true with respectto diode 52 in the circuits of FIGS. 2 and 3.

It will be clear that capacitor 48 of the circuit of FIG. 4 is normallycharged in accordance with voltage drop across resistor 70, whichapplies a sufiiciently positive bias to the grid-cathode circuit of thetube to achieve normal response. Upon interruption in power supply, andthe removal of the voltages supplied by both source 72 and additionalsource 66, capacitor 48 discharges through resistor 70, and throughdiode 52 and cathode resistor 34.

It should be noted that since resistor 34 forms part of one of thedischarge paths for the capacitor, the circuit of FIG. 4 is preferablyused in a system in which the thermistor is associated with anotherstage of the circuit because if resistor 34 is a thermistor, it may inits cold state have a resistance value higher than suitable to achievesubstantially instantaneous discharge of the capacitor. Upon restorationof power supply, control grid 78 of the pentode is maintained at groundpotential by the discharged capacitor 48, which now shunts resistor 70,and through grid leak resistor 26 so that pentode 80 is practicallyinhibited and carries almost no plate current. Once the power supply isrestored, the voltage drop reappears on voltage divider 36 so thatcapacitor 48 is recharged at a comparatively slow rate in accordancewith the long time constant determined by high value resistor 68.Simultaneously, and at the same rate, junction 74 becomes relativelymore positive and the negative bias potential on control grid 78decreases. It can be seen that, in principle, the circuit employing theadditional voltage source 66 operates in a manner which is analogouswith that of the circuits shown in FIGS. 2 and 3.

For practical purposes it should be stated that it is desirable toinhibit one stage of a circuit for a period in the range between 2 and30 seconds, since, with shorter interruptions in supply, thermistors aregenerally still at an elevated temperature, while after periods longerthan 30 seconds the cathodes of conventional tubes are sufficiently coldto prevent output current surges.

It is to be understood that the above-described embodiments areillustrative of the application of the principles of the invention, andnumerous other circuits may be devised by those skilled in the artwithout departing from the spirit and scope of the invention. Thus, byway of example and not of limitation, as stated above, the principle ofthe present invention may be applied to circuits using one single stageand also to multistage circuits. In the case of single stage circuits,the thermistor may form part of the suppressor circuit as symbolized bythe resistor 34 in any one of FIGS. 2, 3, or 4. If, on the other hand,more than one tube or transistor is employed forming distinct stages ofthe circuitry, the thermistor may form part of the circuit of any otherstage, or serve as a coupling element between stages in which caseresistor 34 in any one of FIGS. 2, 3 and 4 may be a standard resistor.It has been pointed out that the power supply for circuits of this typeis generally fed from a network; the symbols for batteries have beenused in the drawing for the purpose of simplification, it being assumedthat the internal impedance of such supplies is relatively low, wherethe supply itself forms part of the capacitor discharge path.

Accordingly, from the foregoing remarks, it is to be understood that thepresent invention is to be limited only by the spirit and scope of theappended claims.

What is claimed is:

1. An electronic circuit including at least one discharge device havingat least one control electrode and a cathode, and a resistive devicecoupled to said cathode, said resistive device having a positivetemperature characteristic, voltage supply means for said dischargedevice, said electronic circuit comprising means for eliminating outputcurrent surges which occur due to the characteristic of said resistivedevice having a positive temperature characteristic and are caused bytransient voltage supply interruptions, said current surge eliminatingmeans including a capacitance and a shunt resistance across it, bothbeing connected in series with said voltage supply and also connected inthe grid-cathode circuit of said discharge device, for supplying throughsaid discharged capacitance a negative cut-off biasing potential to saidcontrol electrode substantially instantaneously upon restoration of thevoltage supply, and means for gradually recharging said capacitance tothereby decrease the biasing potential over a period of timesufficiently long to permit said resistance having a positivetemperature characteristic to return to its normal operating conditions.

2. In an electronic circuit, an electron discharge device having acontrol electrode and a second electrode, at least one resistor having apositive temperature characteristic being coupled to said secondelectrode, means for supplying plate current to the device, and meansfor inhibiting current surges upon restoration of plate current supplysubsequent to short interruption, said surge inhibiting means includingmeans for applying substantially instantaneously a negative cut-offpotential to said control electrode of said device upon restoration ofplat-e current supply, and means for decreasing the negative cut-offpotential at a rate sufiiciently slow to prevent output current surgesresulting from restoration of plate current supply by inhibiting saidelectron discharge device until said resistor returns to its resistancevalue at operating conditions.

3. A surge suppressor according to claim 2, in which said electrode is acontrol grid.

4. A surge suppressor according to claim 2, in which said electrode is asuppressor grid.

5. A system for inhibiting an electron discharge device upon powersupply interruption, said electron discharge device having at least onecontrol electrode and forming one stage of an electrical circuit, saidelectrical circuit including a resistive circuit element having apositive temperature characteristic, the system comprising means forstoring an electric charge during normal operation conditions, means forsubstantially instantaneously discharging the storage means upon powersupply interruption, means energized by the power supply, when it isrestored, for applying a negative cut-off bias to said control electrodeof said electronic discharge device through said discharged storagemeans, and circuit means for gradually decreasing the cut-off bias torestore full output current from the stage to permit the system toreturn to its normal operating conditions.

6. In a surge suppressor, at least two vacuum tubes, each tube formingpart of a distinct stage of a circuit and having at least one controlelectrode, a resistor having a positive temperature characteristiccoupled to one of said tubes, plate current supply means for said tubes,means for applying a negative cut-off potential to one of the controlelectrodes of the other of said tubes substantially instantaneously uponinterruption in plate current supply, and means for decreasing thepotential applied to said electrode of said other tube at a rate of thesame order of magnitude as that of temperature decrease at the cathodeof said one tube and as that of temperature increase of said resistor,whereby output current surges are suppressed.

7. In a surge suppressor for a circuit using vacuum tubes, means forsupplying plate current to the tubes, a temperature-responsive resistorassociated with the cathode branch of the plate circuit of one of thetubes, a capacitor, means for applying a relatively constant potentialto the capacitor under normal operating conditions, means forinstantaneously discharging the capacitor upon interruption of the platecurrent supply, means for applying a negative cut-off grid biasingpotential to one of the tubes through the discharged capacitor, andmeans for comparatively slowly recharging the capacitor to decrease thebiasing potential applied to the grid.

8. In a circuit, at least one vacuum tube, a resistor having a positivetemperature characteristic controlling the output current of saidcircuit, means for supplying plate current to the tube from a networksubject to short interruptions, means for eliminating output currentsurges, :said means comprising a capacitor, means for applying :avoltage which is controlled by the plate current supply to thecapacitor, circuit means having a short time constant for substantiallyinstantaneously discharging the capacitor upon plate current supplyinterruption, means for applying a negative cut-0E biasing potentialthrough the discharged capacitor to the grid of the tube when platecurrent supply is reapplied, and high resistance circuit means forrelatively slowly recharging the capacitor to gradually decrease thecut-off grid potential, whereby full plate current is restored when thepositive temperature characteristic resistor and the tube cathodes havesubstantially reached their ranges of normal operating temperatureconditions.

9. In a vacuum tube circuit including a resistor having a positivetemperature characteristic for controlling the output current, means foreliminating output current surges caused by short power supplyinterruptions, said means comprising a capacitor, a source of supplyvoltage, means including a voltage divider for applying a portion of thesupply voltage to the capacitor, means including a resistor having arelatively low resistance connected across said capacitor forsubstantially instantaneously discharging the capacitor uponinterruption in supply voltage, means for applying a portion of thesupply voltage, when restored, through the discharged capacitor to agrid of one of the vacuum tubes to prevent plate current flow byexcessively biasing the grid, and long time constant circuit meansincluding a relatively high resistor forming part of the voltage dividerfor recharging the capacitor to gradually restore a normally operatingnegative grid bias at a rate substantially corresponding to the rate ofcooling of the cathode of the vacuum tube and of heating of saidresistor.

10. In an operating circuit for a vacuum tube, having at least onecontrol grid, the circuit including a resistor having a positivetemperature characteristic, a power supply having positive and negativesupply lines and an intermediate tap for supplying an intermediatepotential, means for suppressing output surges caused by short powersupply interruptions, said means comprising a voltage divider includinga high-value and a low-value resistor and connected in series across thesupply lines, a capacitor connected across the low value resistor and tothe negative supply line, means connecting said intermediate powersupply tap to the cathode of the tube to apply an appropriateplate-cathode voltage to the tube, a diode for connecting the voltagedivider junction between the resistors and the power supply tap to forman additional discharge path for the capacitor through a portion of thepower supply, the junction between the resistors being connected to saidcontrol grid of the tube, whereby a cutoff biasing potential is appliedto said grid through said capacitor when power is restored followinginterruption, the capacitor thereafter being recharged at acomparatively slow rate through the high value resistor of the voltagedivider, and the biasing potential being gradually decreased untilnormal temperature operating conditions of the tube cathodes and of saidresistor are restored.

11. In an electronic circuit arrangement for eliminating output currentsurges caused by short supply intrruptions and including a resistorhaving a positive temperature characteristic, a vacuum tube having aplate, a cathode, a control grid for receiving signals and a suppressorgrid, means including a positive and a negative lead for supplying powerto the plate circuit of said tube, additional power supply meansconnected in series with said plate circuit supply means, a voltagedivider connected across both power supplies and including acomparatively high value resistor at its positive end and acomparatively low value resistor at its negative end, the junctionbetween said resistors being connected to said suppressor grid toimpress a slightly negative potential on said suppressor grid undernormal operating conditions, a capacitor connected across the low valueresistor of the voltage divider for accumulating a charge in accordancewith the voltage drop appearing across said low value resistor, a diodeconnected between said junction and the negative plate current supplylead for substantially instantaneously discharging the capacitor uponsupply interruption, the capacitor forming a shunt across the low valueresistor, whereby a negative cut-01f biasing potential is impressed onsaid suppressor grid and the capacitor recharges at a comparatively slowrate through said high value resistor of the voltage divider uponrestoration of the power supply, said negative cut-01f biasing potentialdecreasing at the ysame rate until normal operating conditions of saidcathode and said resistor having a positive temperature characteristicare restored.

12. In an electronic circuit arrangement for eliminating output currentsurges caused by short supply interruptions, a vacuum tube having aplate, a cathode and a control grid for receiving signals, meansincluding a positive and a negative lead for supplying power to theplate circuit of said tube, additional power supply means connected inseries with said plate circuit supply means, a voltage divider connectedacross both power supplies and including a comparatively high valueresistor at its positive end and a comparatively low value resistor atits negative end, the junction between said resistors being connected tosaid control grid to impress a slightly negative potential on saidcontrol grid under normal operating conditions, a capacitor connectedacross the low value resistor of the voltage divider for accumulating acharge in accordance with the voltage drop appearing across the lowvalue resistor, a diode connected between said junction and the negativeplate current supply lead for substantially instantaneously dischargingthe capacitor upon supply interruption, the capacitor forming a shuntacross said low value resistor, whereby a negative cut-otf biasingpotential is impressed on said control grid, and the capacitor rechargesat a comparatively slow rate through said high value resistor of thevoltage divider upon restoration of the power supply, said negativecut-off biasing potential decreasing at the same rate until normaloperating conditions are restored.

13. In a surge suppressor for a circuit using vacuum tubes, means forsupplying plate current to the tubes, means including a resistancehaving a positive temperature characteristic for stabilizing operationof said circuit, whereby output voltage surges are caused upon transientvoltage supply interruptions, a capacitor, means for applying arelatively constant potential to the capacitor under normal operatingconditions, means for instantaneously discharging the capacitor uponinterruption of the plate current supply, means for applying a negativecut-oft" grid biasing potential to one of the tubes through thedischarged capacitor, and means for comparatively slowly recharging thecapacitor to decrease the biasing potential applied to the grid.

14. A vacuum tube circuit comprising, means including a resistancehaving a positive temperature characteristic for stabilizing operationof said circuit, whereby output voltage surges are caused upon transientvoltage supply interruptions; and means for eliminating said surgescomprising a capacitor, means for applying a relatively constantpotential to the capacitor under normal operating conditions, means forinstantaneously discharging the capacitor, means for applying arelatively constant potential to the capacitor under normal operatingconditions, means for instantaneously discharging the capacitor uponinterruption of the plate current supply, means for applying a negativecut-off grid biasing potential to one of the tubes of the circuitthrough the discharged capacitor, and means for comparatively slowlyrecharging the capacitor to decrease the biasing potential applied tothe grid.

Reierences Qitcd by the Examiner UNITED STATES PATENTS 2,468,082 4/ 1949Chatterjea et al 330-143 2,758,273 8/1956 Martin 323-41 X 2,826,7343/1958 Miller 323-41 2,831,130 4/1958 Obloy 317-149 2,902,548 9/1959Moeller 330-143 LLOYD MCCOLLUM, Primary Examiner.

1. AN ELECTRONIC CIRCUIT INCLUDING AT LEAST ONE DISCHARGE DEVICE HAVINGAT LEAST ONE CONTROL ELECTRODE AND A CATHODE, AND A RESISTIVE DEVICECOUPLED TO SAID CATHODE, SAID RESISTIVE DEVICE HAVING A POSITIVETEMPERATURE CHARACTERISTIC, VOLTAGE SUPPLY MEANS FOR SAID DISCHARGEDEVICE, SAID ELECTRONIC CIRCUIT COMPRISING MEANS FOR ELIMINATING OUTPUTCURRENT SURGES WHICH OCCUR DUE TO THE CHARACTERISTIC OF SAID RESISTIVEDEVICE HAVING A POSITIVE TEMPERATURE CHARACTERISTIC AND ARE CAUSED BYTRANSIENT VOLTAGE SUPPLY INTERRUPTIONS, SAID CURRENT SURGE ELIMINATINGMEANS INCLUDING A CAPACITANCE AND A SHUNT RESISTANCE ACROSS IT, BOTHBEING CONNECTED IN SERIES WITH SAID VOLTAGE SUPPLY AND ALSO CONNECTED INTHE GRID-CATHODE CIRCUIT OF SAID DISCHARGE DEVICE, FOR SUPPLYING THROUGHSAID DISCHARGED CAPACITANCE A NEGATIVE CUT-OFF BIASING POTENTIAL TO SAIDCONTROL ELECTRODE SUBSTANTIALLY INSTANTANEOUSLY UPON RESTORATION OF THEVOLTAGE SUPPLY, AND MEANS FOR GRADUALLY RECHARGING SAID CAPACITANCE TOTHEREBY DECREASE THE BIASING POTENTIAL OVER A PERIOD OF TIMESUFFICIENTLY LONG TO PERMIT SAID RESISTANCE HAVING A POSITIVETEMPERATURE CHARACTERISTIC TO RETURN TO ITS NORMAL OPERATING CONDITIONS.